System and method of controlling pressure in a surgical tourniquet

ABSTRACT

A system and method of controlling the pressure within a surgical tourniquet so as selectively to occlude blood flow within a portion of a limb of a patient, wherein the pressure within an inflatable cuff surrounding a portion of a limb of a patient is changed by automatically opening a first valve connected to a controller and located within a first conduit between an inflatable bladder and the inflatable cuff, when the pressure in the inflatable cuff is different from that in the inflatable bladder. In another aspect, a system and method of controlling the pressure within a surgical tourniquet so as selectively to occlude blood flow within a portion of a limb of a patient within five seconds. In another aspect, a system and method of detecting a leak in a surgical tourniquet. In another aspect, a surgical tourniquet that, from an inflated state, may enter a deflated state, a set state, a default display state, or an off state. In another aspect, a surgical tourniquet mounted in a housing selectively closed around a pole, wherein the center of gravity of the housing is located within the pole. In another aspect, a surgical tourniquet controlled by means of a graphical user interface. In another aspect, a method of detecting a stuck solenoid valve in a surgical tourniquet.

The present application is a continuation of application Ser. No.09/280,312, file date Mar. 29, 1999 now U.S. Pat. No. 6,051,016.

FIELD OF THE INVENTION

The present invention relates generally to surgical tourniquets. Moreparticularly, the present invention relates to various aspects of asystem and method for controlling pressure in a surgical tourniquet.

BACKGROUND

Surgical tourniquets are widely used during surgical procedures toocclude the flow of blood in a portion of a limb during the procedure,particularly in connection with arthroscopic procedures relating to thehand, wrist, elbow, foot, and knee, in which the existence of abloodless field in the appropriate portion of a patient's limb may berequired. Surgical tourniquets are similarly useful in other proceduresin which the creation of a bloodless field is desirable, including nervegrafting and harvesting. It is particularly important in certainprocedures that a surgeon be able to shut off the flow of bloodextremely quickly during the procedure. Yet prior art surgicaltourniquets typically require seven seconds or more for inflation beforeblood flow may be occluded. It is equally important that pressure beevenly maintained by a surgical tourniquet despite the manipulation by asurgeon of the limb in which blood flow is being occluded by thetourniquet, which manipulation tends to affect the pressure within thetourniquet. It is also important that the surgical tourniquet be easy touse and physically stable so that the surgeon may focus his attention onother aspects of the surgery.

It is therefore an object of the present invention to provide a dualreservoir equilibrium surgical tourniquet allowing swift inflation anddeflation.

It is a further object of the present invention to provide a surgicaltourniquet that can be inflated in less than five seconds.

It is a still further object of the present invention to provide amethod for detecting air leaks in a surgical tourniquet.

It is a still further object of the present invention to provide asurgical tourniquet that from an inflated state may be deflated, resetto default values, adjusted to new values, or turned off.

It is a still further object of the present invention to provide asurgical tourniquet with a housing fitting around a pole and with acenter of gravity within the pole.

It is a still further object of the present invention to provide asurgical tourniquet with an easy to use graphical user interface.

It is a still further object of the present invention to provide amethod for detecting stuck valves in a surgical tourniquet.

SUMMARY OF THE INVENTION

The present invention is directed to a system and method of controllingthe pressure within a surgical tourniquet so as selectively to occludeblood flow within a portion of a limb of a patient. The pressure withinan inflatable cuff surrounding a portion of a limb of a patient isdecreased by automatically opening a first valve connected to acontroller and located within a first conduit between an inflatablebladder and the inflatable cuff, when the pressure in the inflatablecuff is greater than that in the inflatable bladder. The pressure withinan inflatable cuff surrounding a portion of a limb of a patient isincreased by automatically opening a first valve connected to acontroller and located within a first conduit between an inflatablebladder and the inflatable cuff, when the pressure in the inflatablecuff is less than that in the inflatable bladder.

In another aspect, the present invention is directed to a system andmethod of controlling the pressure within a surgical tourniquet so asselectively to occlude blood flow within a portion of a limb of apatient, wherein the pressure within an inflatable cuff surrounding aportion of a limb of a patient is automatically altered by opening afirst valve connected to a controller and located within a first conduitbetween an inflatable bladder and the inflatable cuff, and wherein thepressure within the inflatable cuff may be increased by a pump from apressure equal to that of the surrounding atmosphere to a pressuresufficient to occlude the flow of blood in a portion of the patient'slimb within five seconds.

In another aspect, the present invention is directed to a system andmethod of detecting a leak in a surgical tourniquet, including aninflatable cuff, wherein the pressure of gas within the inflatable cuffis increased until a target pressure is reached. The pressure of gascontained within the inflatable cuff is then repeatedly measured with apressure sensor coupled to the inflatable cuff and connected to acontroller. Data relating to each extraneous change in pressure arestored in a memory. All extraneous changes in pressure are then comparedusing predetermined criteria to determine if a leak has occurred.

In another aspect, the present invention is directed to a surgicaltourniquet, including an inflatable cuff, containing a quantity of gas,and a controller, wherein from an inflated state the surgical tourniquetmay enter a deflated state, a set state, a default display state, or anoff state.

In another aspect, the present invention is directed to a surgicaltourniquet, including an inflatable cuff, a controller connected to theinflatable cuff, and an electronic display connected to the controllerand mounted in a housing selectively closed around a pole, wherein thecenter of gravity of the housing is located within the pole.

In another aspect the present invention is directed to a surgicaltourniquet, including an inflatable cuff, a controller connected to theinflatable cuff, and a display connected to the controller, wherein auser controls the surgical tourniquet by means of a graphical userinterface displayed on said display.

In another aspect, the present invention is directed to a method ofdetecting a stuck solenoid valve in a surgical tourniquet, wherein thecurrent, if any, flowing through the solenoid valve is sensed. It isdetermined whether the solenoid valve is open based on the amount ofcurrent flowing through the solenoid valve. Whether the solenoid valveshould be open is determined based on the current state of the surgicaltourniquet. Whether the solenoid valve is stuck is then determined basedon a comparison of whether the solenoid valve is open and whether itshould be open, and, if the solenoid valve is stuck, any short circuitedoutput is turned off.

In accordance with a further aspect, the present invention is directedto a method for controlling the operation of a surgical tourniquet. Aninput setting is received from a user through a graphicaluser-interface, wherein the input setting corresponds to a user-selectedtarget pressure to be maintained in the surgical tourniquet during amedical procedure. The user-selected target pressure is compared, with acontroller coupled to the user-interface, to a range of acceptabletarget pressures. If the user-selected target pressure is outside of therange of acceptable target pressures, the user-selected target pressureis rejected by the system. Alternatively, if the user-selected targetpressure is within the range of acceptable target pressures, thesurgical tourniquet is pressurized in accordance with the user-selectedtarget pressure.

In accordance with a still further aspect, the present invention isdirected to a further method for controlling the operation of a surgicaltourniquet. In this further method, an input setting is received from auser through a graphical user-interface, wherein the input settingcorresponds to a user-selected time period during which a targetpressure is to be maintained in the surgical tourniquet during a medicalprocedure. The user-selected time period is compared, with a controllercoupled to the user-interface, to a range of acceptable time periods. Ifthe user-selected time period is outside of the range of acceptable timeperiods, the user-selected time period is rejected by the system.Alternatively, if the user-selected time period is within the range ofacceptable time periods, a timer is set in the surgical tourniquet inaccordance with the user-selected time period. An audible alarm is thensounded upon expiration of the user-selected time period. In aparticularly preferred embodiment, a user can optionally delay deflationof the surgical tourniquet for successive predetermined periods of timefollowing expiration of the user-selected period of time by enteringdelay commands through the graphical-user interface. Entry of each delaycommand serves to silence an alarm resulting from expiration of aprevious time period and also serves to reset the timer for a furtherpredetermined time period, after which the alarm sounds again. After apredetermined number of iterations of this process, the system does notaccept further delay commands and the alarm remains in a continuous onstate.

In accordance with yet a further aspect, the present invention isdirected to a still further method for controlling the operation of asurgical tourniquet. An input command is received from a user through agraphical user-interface, wherein the input command corresponds to aninstruction to deflate the surgical tourniquet. Shortly thereafter, thepressure in the surgical tourniquet is sensed and the sensed pressure iscompared with a pressure corresponding to the surgical tourniquet in itsdeflated state. If the sensed pressure exceeds the pressurecorresponding to the surgical tourniquet in its deflated state by morethan a predetermined amount, then an alarm is sounded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the internal pneumatic system ofa surgical tourniquet in accordance with a first preferred embodiment ofthe present invention.

FIG. 2 is a block diagram illustrating a portion of the internalelectronic system of a surgical tourniquet in accordance with a firstpreferred embodiment of the present invention.

FIG. 3 is a flow diagram illustrating the operation of a surgicaltourniquet in accordance with a first preferred embodiment of thepresent invention.

FIG. 4 is a state diagram illustrating the primary states of a surgicaltourniquet in accordance with a first preferred embodiment of thepresent invention.

FIGS. 5A and 5B are block diagrams illustrating the appearance of userinterface elements of a combined display and user input device of asurgical tourniquet in accordance with a first preferred embodiment ofthe present invention.

FIG. 6 illustrates symbols used in a user interface of a surgicaltourniquet in accordance with a first preferred embodiment of thepresent invention.

FIG. 7 is a flow diagram illustrating a method for detecting an air leakin a surgical tourniquet in accordance with a first preferred embodimentof the present invention.

FIG. 8 is a block diagram illustrating circuitry used for detectingstuck valves in a surgical tourniquet in accordance with a firstpreferred embodiment of the present invention.

FIG. 9 is a flow diagram illustrating a method for detecting a stuckvalve in a surgical tourniquet in accordance with a first preferredembodiment of the present invention.

FIGS. 10A through 10H illustrate various views of a housing for portionsof a surgical tourniquet in accordance with a first preferred embodimentof the present invention.

FIG. 11 is a block diagram illustrating the use of the present inventionin an operating room environment in accordance with a first preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following definitions are provided to aid in construing the claimsof the present application:

Default Display State. A state in which default values are displayed ona display. In certain embodiments, the inflatable cuff is deflated andsubsequently re-inflated to a default pressure.

Deflated State. A state in which the pressure within the inflatable cuffdoes not exceed that of the surrounding atmosphere, but in which thesurgical tourniquet has been in an inflated state since the last time inwhich it was in an off state.

Extraneous change in pressure. Any change in pressure within a reservoirthat is not caused by the proper functioning of the valves and pump.Extraneous changes in pressure may be caused either by defects in thesystem, such as air leaks due to holes in reservoirs or air leaks due tovalves failing to close completely (or at all), or by factors externalto the system, such as movement of a patient's limb by a physician.

Gas. Any substance or collection of substances currently predominantlyin a gaseous state. Gas is intended specifically to include ordinaryair.

Inflated State. A state in which the pressure within the inflatable cuffexceeds that of the surrounding atmosphere.

Off State. A state in which the surgical tourniquet can be neitherinflated nor deflated and in which no settings related to the surgicaltourniquet may be altered. The off state is also characterized by aminimal consumption of electrical power.

Ready State. A state in which the surgical tourniquet has completed itssystem test and is ready for inflation, but in which the pressure withinthe inflatable cuff is still equal to that of the surrounding atmosphereand in which no inflation commands have yet been entered.

Reservoir. Any structure capable of containing gas, including suchstructures as an inflatable cuff and an inflatable bladder.

Selecting. The precise meaning of selecting a graphical user interfaceelement depends on the input device and user interface being used. Ifthe user is entering input with a touch screen, selecting an elementtypically means touching it. If the user is entering input with a mouse,selecting an element typically means clicking on it. If the user isentering input with a keyboard, selecting an element typically meanspressing the appropriate key or keys.

Set State. A state in which commands relating to inflation of thesurgical tourniquet may be entered. The inflatable cuff may be eitherinflated or deflated. In certain embodiments, the user interface willnot accept potentially dangerous settings, such as a target pressureabove 450 millimeters of mercury or a time period for occluding bloodflow exceeding two hours.

Startup State. A state in which the surgical tourniquet runs varioustests to ensure that it is working properly and in which the surgicaltourniquet automatically fills its internal bladders to certain defaultpressures.

System Failure State. A state in which an error condition prevents theproper functioning of the system. Depending on the error conditionencountered, the system may either enter an off state immediately orcontinue to function at least partially during the current operationbefore entering an off state.

Referring now to FIG. 1, the internal pneumatics of a preferredembodiment of the surgical tourniquet are illustrated. Two cuffs, 102Aand 102B, are shown, as well as subsystems relating to each. In order tosimplify the following discussion, only cuff 102A will be furtherdescribed; however, the following description relates equally to cuff102B and the system components relating to it. Moreover, although twocuffs are shown in FIG. 1, a surgical tourniquet in accordance with thepresent invention may have only one cuff, or may have more than twocuffs.

Cuff 102A is an inflatable device capable of being placed around a limbof a patient, much as a blood pressure cuff is placed around the arm ofa patient whose blood pressure is being measured. It is connected bytubing, that runs partially within manifold 108 to valves 110A, 112A,114A, and 116, sensors 104A and 106A, pump 118, and equilibrium bladder120A. Pump 118 is used to pump gas into the system. Many gases may beused, but in the embodiment here illustrated, ordinary air from thesurrounding atmosphere is used for reasons of cost and simplicity. Theair is pumped through one way valve 116, which always allows air to bepumped into the system, but does not allow air to flow back to the pump.In other embodiments one way valve 116 may be a standard valve that mustbe opened and closed as appropriate, or may be omitted altogether. Theuse of a one way valve, however, prevents air from escaping from thesystem upon failure of side valve 114, permitting pressure to bemaintained in the inflatable cuff until the completion of the currentsurgical procedure.

Opening side valve 114A allows air to be pumped through into equilibriumbladder 120A, while closing side valve 114A prevents air from flowingfrom the pump to equilibrium bladder 120A. In a single cuff systemincluding a valve between the pump and the manifold, a side valve is notneeded. However, in a multiple cuff system, the use of side valvesallows the pressures in the several cuffs to be changed independently ofeach other by pumping air through one or more open side valves while oneor more other side valves are closed. Side valve 114A is also connectedby tubing to equilibrium bladder 120A, cuff valve 110A, exit valve 112A,and bladder sensor 106A. Thus any air pumped into the system throughside valve 114A will always be able to flow freely to equilibriumbladder 120A and bladder sensor 106A. Moreover, air always flows freelybetween equilibrium bladder 120A and bladder sensor 106A, resulting inthe pressures of equilibrium bladder 120A and bladder sensor 106A beingequal, except possibly for minute periods of time when the system is notin an equilibrium state.

Cuff valve 110A, which is connected to tubing leading to cuff 102A andcuff sensor 104A from tubing leading to equilibrium bladder 120A, exitvalve 112A, side valve 114A, and bladder sensor 106A, functions toseparate cuff 102A and cuff sensor 104A from equilibrium bladder 120Aand bladder sensor 106A, and to allow different pressures to bemaintained in the cuff and bladder whenever the cuff valve is closed.Opening the cuff valve, on the other hand, will swiftly equalize thepressures in the cuff and equilibrium bladder. The free flow of airbetween cuff 102A and cuff sensor 104A allows the pressures at cuff 102Aand cuff sensor 104A to be almost always almost precisely equal.

Opening exit valve 112A allows air to flow freely between equilibriumbladder 120A and the surrounding atmosphere, resulting in the pressurewithin the equilibrium bladder being reduced to that of the surroundingatmosphere almost immediately. Moreover, if cuff valve 110A and exitvalve 112A are both open at once, air may flow freely between thesurrounding atmosphere and the cuff as well, resulting in the pressurewithin the cuff being reduced to that of the surrounding atmospherealmost immediately.

Turning now to FIG. 2, a portion of the internal electronic system of apreferred embodiment of the present invention is illustrated. Controller202, which includes a timer, is connected to display 204, memory 206,sensors 104A, 104B, 106A, and 106B, valves 110A, 110B, 112A, 112B, 114A,and 114B, and pump 118. The controller is able through software to turnon and off the pump as needed, to open and close the valves as needed,to monitor the sensors, to store data in the memory and to retrieve itas needed, and to communicate with the user via the display (whichincludes an input device in this embodiment).

Referring to FIG. 3, a preferred embodiment of a method of controllingthe pressure within a cuff of a surgical tourniquet is illustrated. Thismethod is implemented in software on controller 202. In step 300, atarget pressure is accepted from a user, as will be discussed below inconnection with FIGS. 5A, 5B, and 6. Although the following descriptionrefers to only one cuff, it is to be understood that target pressuresfor multiple cuffs may be accepted in step 300 and each following stepmay be performed separately with regard to each cuff. A common targetpressure is 300 millimeters of mercury, which is sufficient to occludeblood flow in a vein. In the preferred embodiments, the user interfacewill not accept a pressure exceeding 450 millimeters of mercury, whichis generally considered to be unsafe. In step 302, a time period duringwhich the target pressure is to be maintained is entered by the userthrough an input device, as is also discussed below in connection withFIGS. 5A, 5B, and 6. Normally, the time period will not exceed twohours, which is accepted as the maximum safe period during which bloodflow may be occluded in a portion of a limb of a patient. In thepreferred embodiments, the input device will not initially accept a timeperiod exceeding two hours; however, the user may override the two hourlimitation for an additional thirty minutes in five minute increments.

Although step 304 is depicted as occurring between steps 302 and 306, itin fact occurs repeatedly and continually throughout the process in thepreferred embodiments. In step 304, controller 202 queries sensors 104and 106 to determine the current pressures in the cuff and relatedequilibrium bladder.

In step 306, the equilibrium bladder is inflated to an appropriatepressure (or partially or entirely deflated if already inflated to anexcessive pressure). This value depends on the target pressure, thecurrent pressure in the cuff, and the relative volumes of the cuff andequilibrium bladder, including all related tubing (related tubing beingtubing connected to the reservoir in question without being separatedfrom it by a valve) and is given by the following equation in certainpreferred embodiments:$P_{B} = {{P_{T}\quad \left( {1 + \frac{V_{C}}{V_{B}}} \right)} - {P_{C}\left( \frac{V_{C}}{V_{B}} \right)}}$

where P_(T) is the target pressure for the cuff, P_(B) is the pressureto which the bladder should be inflated, P_(C) is the current pressurein the cuff, V_(B) is the volume of the bladder including all relatedtubing, and V_(C) is the volume of the cuff including all relatedtubing. As an example, if the user entered a target pressure of 300millimeters of mercury in step 300, the cuff and equilibrium bladderwere determined to both be filled with air at the pressure of 30millimeters of mercury, and the volumes of the cuff and equilibriumbladder, including all related tubing, were equal, the equilibriumbladder would be inflated to a pressure of 570 millimeters of mercury.

In order to inflate the equilibrium bladder, the controller closes cuffvalve 110 and exit valve 112, if open, and opens side valve 114, ifclosed. It then operates pump 118 and continuously monitors the pressureat bladder sensor 106 until the pressure measured by that sensor equalsthe appropriate pressure, which is 570 millimeters of mercury in theabove example. At that point, the controller closes side valve 114 andceases to operate pump 118.

The system could immediately proceed to execute step 308; however, inthe preferred embodiment disclosed herein, the system waits betweensteps 306 and 308 until the user signals the system to proceed throughthe input device, as is discussed below in connection with FIGS. 5A, 5B,and 6. This allows a user to inflate the bladder ahead of time at anypoint during preparations for a surgical procedure and subsequentlyinflate the cuff almost instantaneously, that is to say in a smallfraction of a second, at the appropriate point in the surgicalprocedure, so that blood flow is occluded for the minimum necessaryinterval of time.

In step 308, the system, either immediately or when ordered to,equalizes pressure between the equilibrium bladder and the cuff. Thecontroller accomplishes this simply by opening cuff valve 110. At thispoint, the target pressure is achieved in the cuff, and the system canawait further user input in step 310. In the preferred embodiment,however, the system continues to monitor and adjust the cuff pressurewhenever the cuff is inflated. A small air leak may lead to a gradualloss of pressure. In addition, a surgeon's manipulation of a patient'slimb may cause external pressure to be placed on the cuff or relieved,thereby altering the internal pressure of the cuff. In the preferredembodiment, the system continuously monitors such changes and adjuststhe pressure of the cuff to maintain a pressure as close as possible tothe target pressure and within predefined limits of the target pressurein much the same way as the system adjusts such pressure if the useralters the target pressure in step 310.

In an alternative embodiment, step 308 can be performed before step 306is completed. For example, the cuff valve might be opened when thepressure within the equilibrium bladder had reached two-thirds of thepressure necessary to inflate the inflatable cuff to the targetpressure. The pump would then continue to operate until both theequilibrium bladder and the inflatable cuff reached the target pressure.This embodiment offers greater assurance that the inflatable cuff willnot be over-inflated and offers a degree of control over the speed ofinflation.

If the user enters a higher desired pressure in step 310, the controllercan simply open side valve 114 and operate pump 118 until the pressuresmeasured at sensors 104 and 106 are equal to the target pressure. In thepreferred embodiment, however, cuff valve 110 is closed before sidevalve 114 is opened, and the system returns to step 306, in order toallow a user to enter an altered target pressure before the moment atwhich the change is desired, allowing the system to achieve a new targetpressure almost instantaneously when the desired moment of changearrives. Pump 118 is operated until an appropriate pressure is reachedin the equilibrium bladder, as measured by the bladder sensor. Theappropriate pressure is determined using the same equation as in step306. To continue with the above example, if the user entered a targetpressure of 320 millimeters of mercury, the equilibrium bladder would beinflated to a pressure of 340 millimeters of mercury. The controllerthen closes side valve 114 and opens cuff valve 110 in step 308, therebyequalizing pressures between the equilibrium bladder and the cuff andalmost instantaneously achieving the target pressure.

Returning to step 310, if the user instead (or later) enters a lowertarget pressure, the system proceeds to step 312 in which the cuff andthe equilibrium bladder are totally or partially deflated one or moretimes. In the preferred embodiment, the cuff valve is kept open whilethe exit valve is also opened to allow air to escape from both the cuffand the equilibrium bladder until the target pressure is measured at thecuff sensor, at which time the exit valve is closed. In otherembodiments, however, the cuff valve might first be closed and theequilibrium bladder then partially or totally deflated prior to closureof the exit valve and equalization of pressures between the cuff and theequilibrium bladder through opening of the cuff valve. Doing so,however, requires multiple stages of deflation in certain instances inwhich relatively large declines in pressure are required, depending onthe relative volumes and pressures of the cuff and equilibrium bladder.The system then returns to step 310.

Next, in step 314, the controller checks whether the time period enteredin step 302 (which may have been modified in step 310) has expired. Ifthis time period has expired, the system continues to step 316. If not,the system returns to step 304, so that the pressure within the cuff maybe repeatedly measured, deviations from the target pressure may becorrected, and the user may be prompted for further input throughout thesurgical procedure. Pressure readings in step 304 might be taken onceper second in a preferred embodiment, but may be taken more or lessfrequently depending on system requirements and resources.

Finally, in step 316, when the time period entered in step 302 (whichmay have been modified in step 310) has expired, exit valve 112 isopened and the pressures within both the cuff and the equilibriumbladder are equalized with that of the surrounding atmosphere. In thepreferred embodiments, however, the exit valve is not immediately openedat the end of the time period, but rather an alarm is sounded, which maybe overridden by the user. If the user fails to override the alarmwithin a predetermined period of time, the exit valve is opened and thecuff is deflated. However, by overriding the alarm, the user can delayautomatic deflation for additional periods of time. In no case, however,in the preferred embodiments, will the user be permitted to continuouslyocclude the flow of blood in a portion of a patient's limb for a periodof time exceeding two hours and thirty minutes.

Referring to FIG. 4, the primary states in the preferred embodiment inwhich the system may be are illustrated. Initially, the system is in offstate 400. From this state, the system may enter startup state 402. Inthe preferred embodiment disclosed herein, a user may cause the systemto enter the startup state from the off state by pressing on/off button524 illustrated in FIG. 5A. Although not shown in FIG. 4, a user maycause the system to reenter off state 400 from any other system state bypressing on/off button 524 at any time that the system is not in the offstate.

While the system is in startup state 402, it executes a system test. Ifeach component of the system test is satisfactorily completed, thesystem enters ready state 404; otherwise, it enters system failure state406. During startup, the system will determine, inter alia, whether thecurrent equilibrium bladders have been inflated an excessive number oftimes, rendering bladder failure likely, by monitoring a counter that isincremented every time the bladders are inflated. If the bladders havebeen inflated an excessive number of times, the system will enter thesystem failure state and a service icon will be illuminated. Inaddition, the system increments a counter each time it enters thestartup state without subsequently entering the ready state. If thecounter exceeds a predetermined limit (most likely due to softwarefailure), the system will likewise enter the system failure and aservice icon will be illuminated. From state 406, the system may beturned off and subsequently repaired. Although not shown, the system mayenter the system failure state from any other state at any time upon theoccurrence of any major component failure preventing the correctoperation of the system.

From state 404, in addition to being able to enter states 400 and 406,as discussed above, the system may enter any of states 408, 410, or 412,depending on the actions of the user of the system. If the user pressesdefault display button 522 in FIG. 5A, the system enters default displaystate 408 in which it displays the default time and pressure settingsfor the system, as originally set in the factory, or as since modifiedby a user. The system also deflates the cuffs and equilibrium bladders.

In set state 410, the user is able to set time and pressure settings forthe cuffs for a surgical procedure, and also to set default values forthose settings, as described below in connection with FIG. 5A. Ininflate state 412, the system inflates the cuffs to the target pressuresset in step 410 or the current default pressures previously displayed instep 404 or step 408 (or both), as may be applicable. In deflate state414, the system deflates the cuffs and equilibrium bladders so that thepressures within such reservoirs are equal to that of the surroundingatmosphere, but the system does not alter the set times and pressures.Thus, the user may re-inflate each cuff with the touch of a button(518).

From any of default display state 408, set state 410, inflate state 412,or deflate state 414, the user may cause the system to enter any ofdefault display state 408, set state 410, inflate state 412, or deflatestate 414 by pressing the appropriate buttons, 522 in the case ofdefault display state 408, any of 508, 510, 514, or 516 in the case ofset state 410, 518 in the case of inflate state 412, or 520 in the caseof deflate state 414, all as shown in FIG. 5A and described below. Theuser may also cause the system to enter the off state, as discussedabove.

Referring now to FIG. 5A, an exemplary display incorporating a graphicaluser interface is shown. The display includes four areas for informationto be displayed and several sets of buttons. Regions 502A and 502Bdisplay data relating to the proximal and distal cuffs respectively.Each of the two display areas is divided into an upper region in whichdata relating to the amount of time that the appropriate cuff will bepressurized is set forth and a lower region in which data relating tothe pressure to be achieved in the appropriate cuff is displayed. Theupper area can be configured to show either the amount of time duringwhich the appropriate cuff has been inflated or the amount of timeremaining until the cuff is deflated, in either case in both textual andgraphical form. The temporal graphical element is in the form of twoconcentric segmented circles, with each segment of each circlerepresenting a portion of an hour. As time elapses, segments are eitherilluminated or turned off, depending on the configuration. The lowerarea shows the current pressure when in an inflated state (or thepressure to be achieved in other states) in both textual and graphicalform. As can be seen from FIG. 5B, the graphical pressure element is inthe form of a rounded, inverted, segmented cone bisected by an ellipse.When the system is in an inflated state and the pressure in the cuff isequal to the target pressure, the ellipse and all segments below it areilluminated, as is shown in FIG. 5A. When the system is in an inflatedstate but the cuff pressure is below the target pressure, fewer segmentsare illuminated. When the system is in an inflated state but the cuffpressure is above the target pressure, more segments are illuminated.Thus, the user can determine at a glance whether the cuff is at thetarget pressure without the need for mental computations.

Region 504, which is located between regions 502A and 502B, and region506, which is located below regions 502A, 502B, and 504, are used todisplay icons conveying information about the system to the userthereof. These icons are discussed below in connection with FIG. 6.

Buttons 508A, 510A, 512A, 514A, 516A, 518A, and 520A relate to theproximal cuff, while buttons 508B, 510B, 512B, 514B, 516B, 518B, and520B relate to the distal cuff. Buttons 522 and 524 relate to bothcuffs. Buttons 508A and 508B may be used while in a set state toincrease the amount of time that a cuff will be inflated in five minuteincrements, while buttons 510A and 510B may be used to decrease theamount of time that a cuff will be inflated in five minute increments.Similarly, buttons 514A and 514B may be used while in a set state toincrease the pressure of a cuff once it is inflated in five millimeterof mercury increments, while buttons 516A and 516B may be used while ina set state to decrease the pressure of a cuff once it is inflated infive millimeter of mercury increments. Buttons 512A and 512B may then beused to save the changed values, causing the cuff to be inflated ordeflated, as discussed in connection with FIG. 3. The failure to pressbuttons 512A and 512B will result in changes to the settings relating tothe corresponding cuffs being discarded upon the system's exit from theset state. The user will receive an audible caution in this case toindicate that the changes have been discarded. Settings may additionallybe saved as default settings by holding down the appropriate inflatebutton, 518A or 518B, and then pressing the appropriate set button, 512Aor 512B. A user may change the default settings from the factory setsettings if the user commonly employs different pressure settings insurgical procedures. For example, a specialist in pediatric surgerywould likely employ lower pressures than surgeons performing surgerieson adults.

Buttons 518A and 518B are used to inflate the respective cuffs using thelast saved pressure and time duration values. Buttons 520A and 520B arecorrespondingly used to deflate the respective cuffs. Button 522 causesthe system to enter the default display state and sets all values to thelast saved default values (which, if the system is in the inflated statecauses the cuff to be inflated to the default pressure), while button524 toggles the system between on and off states.

FIG. 5B shows the display with a maximum number of icons shown.Depending on the circumstances, icons may be shown in any or all ofregions 502A, 502B, 504, or 506. An alarm icon (not shown) is alsodisplayed on top of the system in green whenever the system is on and inred whenever an alarm condition is currently occurring.

FIG. 6 shows the icons in alphabetical order. Alarm emergency icon 602is shown whenever the system is significantly malfunctioning, such aswhen there is a major air leak, or when there is software ormicroprocessor failure.

Alarm sound off icon 604 is shown when the user has continued to operatethe cuff in an inflated state after the conclusion of the specifiedperiod for inflation.

Air leak icon 606 is shown whenever an air leak occurs, whether the leakis a major leak requiring immediate system shutdown or a minor leak thatneed not be addressed until after the completion of any pending surgicalprocedure. If the air leak has been identified as relating exclusivelyto one of the cuffs, the air leak icon will be shown on the side of thedisplay relating to that cuff. Otherwise, the icon will be shown in themiddle of the display.

Battery charging icon 608 is shown whenever the battery lacks sufficientpower to begin a procedure. No procedure will be started without a fullbattery, which may require prolonged charging.

Battery icon 610 is shown whenever the system is operating on battery,rather than ac current.

Caution icon 612 is shown whenever illegal input has been received, suchas when an unduly high pressure or period of time has been entered (andrejected) or when data has been entered in the wrong order. Audiblefeedback is also provided.

Cuff pressurized icon 614 is shown whenever a cuff is inflated when thesystem is not in an inflated state. Typically, this occurs after a powerfailure during an inflated state.

Deflated icon 618 is shown whenever a cuff is in a deflated state.

Ready icon 628 is shown whenever the system is in a ready state.

Default display icon 630 is shown whenever the system is in a defaultdisplay state.

Service icon 632 is shown whenever the system requires service, whetheror not it can be used to complete any pending surgical procedure.

Testing icon 636 is shown whenever the system is executing system testsas part of its startup procedure.

One of time count up 640 and time count down 638 icons is showndepending on whether the timer mode has been set to count up or countdown. In time count down mode, the system displays the amount of timeremaining before the appropriate cuff will be deflated. In time count upmode, the system displays the amount of time that the cuff has alreadybeen inflated.

In the preferred embodiments, the user interface is designed not only todisplay information concerning the current state of the surgicaltourniquet in an easy to comprehend manner but also to reject illegal orinappropriate input in a manner that informs the user of the surgicaltourniquet that such input has been rejected. As discussed above, theuser interface will not accept a pressure above 450 millimeters ofmercury or a time period initially exceeding two hours and will giveaudible feedback when rejecting such input. In addition, the surgicaltourniquet will give audible feedback when inappropriate state changesare attempted, such as inflating from an inflated state, and when thesystem fails to respond correctly to proper input, such as when thesystem is unable to deflate due to a stuck valve. In some embodimentsthe audible feedback will be in the form of beeps or similar sounds, butin other embodiments, the audible feedback may be in the form ofprerecorded or computer generated messages in English or otherlanguages.

Turning now to FIG. 7, a method of detecting an air leak in the surgicaltourniquet is illustrated. In step 700, a cuff is inflated to anappropriate pressure. Steps 702 through 706 are then repeatedlyperformed until the cuff is deflated. In step 702, the controllermeasures the pressure within the cuff by monitoring a cuff sensor andstores each measurement in memory. The controller also stores theoccurrence of any opening or closing of a valve or the operation of thepump. In step 704 the controller first establishes whether a change inpressure has been detected, second establishes whether any such changewas extraneous in nature, and third stores all data relating to suchchange if extraneous in nature.

The controller establishes whether a change in pressure has beendetected by comparing the current pressure measurement with the previouspressure measurement relating to that cuff. The controller thendetermines whether the change in pressure was extraneous by checkingwhether any valve openings or closings, or the operation of the pump,should have caused the pressure change. If not, any change isextraneous. Then, the controller stores in the memory data relating toany such extraneous changes.

In step 706, the controller determines if a leak is occurring bycomparing the data relating to extraneous changes stored in alliterations of step 704 with predetermined criteria. For example, thecontroller might determine that a leak was occurring if the absolute orpercentage decrease in pressure due to extraneous reasons from onepressure reading to the next or within a given period of time wasgreater than a predetermined amount or percentage. In addition, thecontroller might determine that a leak was occurring if more than apredetermined percentage of all or a first predetermined number of asecond predetermined number of extraneous changes in pressure weredecreases in pressure. The controller might also determine that a leakwas occurring if the slope of the pressure within the cuff during anyperiod in which no non-extraneous changes in pressure had occurred wasnot zero, or was negative, or was less than some (negative) number.

Referring to FIG. 8, a system for detecting a stuck valve isillustrated. A valve, which may be any of cuff valves 110A and 110B,exit valves 112A and 112B, side valves 114A and 114B, and one way valve116, is connected both to controller 202 and to stuck valve detectioncircuit 802, which in turn is also connected to controller 202. In thepreferred embodiments, each valve is a solenoid valve and each valve isconnected to a stuck valve detection circuit, which is available fromMotorola as MC33293A.

Referring to FIG. 9, a method of detecting a stuck valve in a surgicaltourniquet is illustrated. In step 900, the current flowing through thevalve, if any, is detected by the stuck valve detection circuit. In step902, the controller measures the current flowing through the circuit anddetermines whether the valve is open based on the amount of currentflowing through the circuit. In step 904, the controller determineswhether the valve should be open based on the state of the surgicaltourniquet. For example, in an inflated state the exit and side valveswould ordinarily be closed and the cuff valve open. In step 906, thecontroller compares whether the valve is open with whether the valveshould be open. If the valve is open and should be open, or is closedand should be closed, the controller concludes that the valve is notstuck and returns to step 900 and continues to monitor the valve. If, onthe other hand, the valve is open but should be closed, or is closed butshould be open, the controller determines that the valve has failed,causes the system to enter a system failure state, and optionallyindicates to the user the existence of a short circuit through visual oraudible signals, or both.

Referring to FIGS. 10A through 10H, a housing 1002 containing display204, equilibrium bladders 120A and 120B, and most of the components ofthe surgical tourniquet other than the cuffs, is illustrated. Takentogether, FIGS. 10A (front view), 10B (side view), and 10C (rear view)illustrate that housing 1002 can be situated on a pole 1004 so that thepole runs through the center of the housing and the center of gravity ofthe housing is within the pole. This center of gravity provides thehousing with greater stability than prior art systems, which attachedexternally to poles, but had centers of gravity within the housings butnot within the poles. The configuration of the present invention alsooffers the advantage of conserving space.

FIGS. 10D and 10E are side and front cut-away views of the housingindicating the locations of the equilibrium bladders 120. FIGS. 10F,10G, and 10H are front, side, and rear views respectively of the housingrevealing interior components.

Referring now to FIG. 11, the placement of a cuff 102 around a limb of apatient 1102 is illustrated as well as the placement of the housing 1002relative to a user 1104 of the surgical tourniquet.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes of the invention.Accordingly, reference should be made to the appended claims, ratherthan the foregoing specification, as indicating the scope of theinvention.

What is claimed is:
 1. A surgical tourniquet system, including an inflatable cuff that may be closed around a patient's limb so as to exert pressure on blood vessels within a portion of the limb, comprising; an inflatable cuff containing a first quantity of gas having a first internal pressure; an inflatable bladder containing a second quantity of gas having a second internal pressure; a first conduit between said inflatable cuff and said inflatable bladder; a first valve within said first conduit; and a controller connected to said first valve, wherein, when the pressure in said inflatable cuff is greater than that in said inflatable bladder, said controller decreases the pressure in said inflatable cuff by opening said first valve; and wherein, when the pressure in said inflatable cuff is less than that in said inflatable bladder, said controller increases the pressure in said inflatable cuff by opening said first valve.
 2. The surgical tourniquet system of claim 1, further comprising: a pump connected to said controller; a second conduit between said pump and said inflatable bladder; a second valve within said second conduit and connected to said controller, wherein said controller increases the pressure in said inflatable bladder by opening said second valve and pumping gas from outside the surgical tourniquet system into said inflatable bladder; and wherein said controller decreases the pressure in said inflatable bladder by opening said second valve, thereby equalizing the pressure in said inflatable bladder with that of the atmosphere.
 3. A method of controlling the pressure within a surgical tourniquet system so as selectively to occlude blood flow within a portion of a limb of a patient, comprising the steps of: (a) decreasing the pressure within an inflatable cuff surrounding a portion of a limb of a patient by automatically opening a first valve connected to a controller and location within a first conduit between an inflatable bladder and the inflatable cuff, when the pressure in the inflatable cuff is greater than that in the inflatable bladder, and (b) increasing the pressure within an inflatable cuff surrounding a portion of a limb of a patient by automatically opening said first valve connected to a controller and located within a first conduit between an inflatable bladder and the inflatable cuff, when the pressure in the inflatable cuff is less an that in the infltable bladder.
 4. A surgical tourniquet system, comprising: an inflatable cuff containing a first quantity of gas having a first internal pressure; an inflatable bladder containing a second quantity of gas having a second internal pressure; and controller means for equalizing the first and second internal pressures.
 5. A method of detecting a leak in a surgical tourniquet system, including an inflatable cuff, comprising the steps of: (a) first, increasing the pressure of gas within the inflatable cuff until a target pressure is reached; (b) thereafter, measuring the pressure of gas contained within the inflatable cuff with a pressure sensor coupled to the inflatable cuff and connected to a controller, said measurements being made repeatedly while said inflatable cuff is pressurized; (c) storing data relating to each pressure measurement in a memory, and (d) comparing each pressure measurement using predetermined criteria to determine if a leak has occurred.
 6. The method of claim 5, wherein step (d) comprises determining that a leak has occurred if the percentage decrease in pressure due to an extraneous change in pressure exceeds a predetermined percentage.
 7. A method in accordance with either of claim 5 or 6, further comprising the step of: (e) emitting an audible alarm if a leak was determined to have occurred in step (d).
 8. A surgical tourniquet system, comprising: an inflatable cuff, containing a quantity of gas; a controller; a pressure sensor coupled to said inflatable cuff and connected to said controller, said pressure sensor measuring the pressure in said cuff; and a memory connected to said controller, where the controller determines whether a leak has occurred by continuously comparing pressure measurements from said pressure sensor to predetermined criteria.
 9. A system for detecting a leak in a surgical tourniquet system, including an inflatable cuff, comprising: (a) means for increasing the pressure of gas within the inflatable cuff until a target pressure is reached; (b) means for repeatedly measuring the pressure of gas contained within the inflatable cuff with a pressure sensor coupled to the inflatable cuff and connected to a controller; (c) means for storing data relating to each extraneous change in pressure in a memory; and (d) means for continuously comparing pressure measurements from said means for repeatedly measuring the pressure of gas contained within the inflatable cuff using predetermined criteria to determine if a leak has occurred.
 10. A surgical tourniquet system comprising an inflatable cuff and a controller, said inflatable cuff containing a quantity of gas, wherein said surgical tourniquet system functions in a set of states including an inflated state, a deflated state, a set state, a default display state, and an off state, wherein an operator may define parameters identifying a desired inflatable cuff condition when surgical tourniquet system is in said set state; wherein from an inflated state the surgical tourniquet system may enter a deflated state; wherein from an inflated state the surgical tourniquet system may enter a set state; wherein from an inflated state the surgical tourniquet system may enter a default display state; wherein from an inflated state the surgical tourniquet system may enter an off state; and wherein from said set state the surgical tourniquet system may enter an inflated state in which the quantity of gas in the inflatable cuff is varied to conform with parameters identified in said set state prior to said inflated state.
 11. The surgical tourniquet system of claim 10, wherein from a deflated state the surgical tourniquet system may reenter a previous inflated state in which the pressure exerted by the surgical tourniquet system on blood vessels in the limb of a patient is identical to the pressure previously exerted on the blood vessels before deflation of the surgical tourniquet system; wherein from a deflated state the surgical tourniquet system may enter a set state; wherein from a deflated state the surgical tourniquet system may enter a default display state; and wherein from a deflated state the surgical tourniquet system may enter an off state.
 12. A surgical tourniquet system comprising an inflatable cuff and a controller, said inflatable cuff containing a quantity of gas, wherein said surgical tourniquet system function in a set of states including an inflated state, a deflated state, a set state, a default display state, and an off state, wherein an operator may define parameters identifying a desired inflatable cuff condition when surgical tourniquet system is in said set state; wherein from an inflated state the surgical tourniquet system may directly enter a deflated state; wherein from an inflated state the surgical tourniquet system may directly enter a set state; wherein from an inflated state the surgical tourniquet system may directly enter a default display state; and wherein from an inflated state the surgical tourniquet system may directly enter an off state; and wherein from said set state the surgical tourniquet system may enter an inflated state in which the quantity of gas in the inflatable cuff is varied to conform with parameters identified in said set state prior to said inflated state.
 13. The surgical tourniquet system of claim 12, wherein from a deflated state the surgical tourniquet system may directly reenter a previous inflated state in which the pressure exerted by the surgical tourniquet system on blood vessels in the limb of a patient is identical to the pressure previously exerted on the blood vessels before deflation of the surgical tourniquet system; wherein from a deflated state the surgical tourniquet system may directly enter a set state; wherein from a deflated state the surgical tourniquet system may directly enter a default display state; and wherein from a deflated state the surgical tourniquet system may directly enter an off state.
 14. A surgical tourniquet system, comprising: an inflatable cuff; a controller connected to said inflatable cuff; and a display connected to said controller; wherein a user controls the surgical tourniquet system by means of a graphical user interface displayed on said display; wherein the graphical user interface comprises a plurality of icons.
 15. The surgical tourniquet system of claim 14, wherein the plurality of icons comprises an air leak icon displayed to indicate a gas leak in the surgical tourniquet system; and wherein the air leak icon includes a representation of a broken geometric shape and a representation of a gas cloud.
 16. The surgical tourniquet system of claim 14, wherein the plurality of icons comprises a cuff pressurized icon displayed to indicate that said cuff is currently pressurized; and wherein the cuff pressurized icon includes a representation of a geometric shape and a plurality of representations of arrows.
 17. The surgical tourniquet system of claim 14, wherein the plurality of icons comprises a deflated icon displayed to indicate that said cuff is currently deflated; and wherein the deflated icon includes a representation of a pinched broken geometric shape and a representation of a gas cloud.
 18. The surgical tourniquet system of claim 14, wherein the plurality of icons comprises an inflated icon displayed to indicate that said cuff is currently inflated; and wherein the inflated icon includes a representation of an unbroken geometric shape.
 19. The surgical tourniquet system of claim 14, wherein the plurality of icons comprises a default display icon displayed to indicate that said cuff is currently in a default display state; and wherein the default display icon includes a representation of the letter “d”.
 20. The surgical tourniquet system of claim 14, wherein the plurality of icons comprises a time count down icon displayed when the cuff is in an inflated state to indicate the approximate amount of time during which said cuff is to remain pressurized; wherein the time count down icon includes a representation of at least one hand of a clock and a representation of an outline of a face of a clock; wherein a first portion of the representation of the outline of the face of the clock is a solid line; wherein a second portion of the representation of the outline of the face of the clock is a broken line; and wherein the length of the first portion of the representation of the outline of the face of the clock is related to the amount of time remaining during which said inflatable cuff is to remain pressurized.
 21. The surgical tourniquet system of claim 14, wherein the plurality of icons comprises a time count up icon displayed when the cuff is in an inflated state to indicate the approximate amount of time during which said cuff has been in an inflated state; wherein the time count up icon includes a representation of at least one hand of a clock and a representation of an outline of a face of a clock; wherein a first portion of the representation of the outline of the face of the clock is a solid line; wherein a second portion of the representation of the outline of the face of the clock is a broken line; and wherein the length of the first portion of the representation of the outline of the face of the clock is related to the amount of time during which said inflatable cuff has been in an inflated 